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Old 03-04-2005, 12:33 AM
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Another GM 'Body' question

Reading through the thread on GM body designs inspired me to ask something I have always wondered.

Are there any major dimensional differences of major body elements between converts, hardtops, 4dr and 2dr sedans within a particular body line?

To me the roofline of a hardtop has always looked slightly sleeker than a 4dr or 2dr sedan for instance, often I know rear glass can be different but I would like to know if the sleeker appearance is more to do with the fact there are no pillars and such or actually due to a major difference in the actual lines of the roof.

Also, it often appears that a hardtop roof meets the body at the rear in a different place to the sedans, making me think hardtops and convertibles have longer trunk lids, I doubt this can be the case because as far as I know the rear seat must be in the same place for all models, so the roof can't come back that much shorter than a sedan, it is probably all optical illusion.

I ask because I am wanting to convert my '54 Chevy 4dr sedan into a 2dr convertible (actually a retractable hardtop) and I am wondering if my "fake" convertible will differ in any major way from the factory convertible, at least visually from the outside. I know of course there will be all kinds of structural differences.

I am also wondering if my converted 4dr sedan roof will be all that different from an original hardtop roof as far as it's lines and appearance are concerned(apart from the rear glass of course). I stare and stare at pictures of the '54 hardtop, convertible and 4dr sedan, and can never quite make my mind up as to where there are major differences and where I am just seeing things.
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Old 03-04-2005, 05:49 AM
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In the GM line. The hardtop and convertable windshields tend to be similar if not the same. In the later years, the four door sedans have different windshields that are taller and at a slight different angle. Very noticable in the "G" body line for example.

If you check the archives of this forum you will find a four door fifties Chevy that has been converted to a two door hard top. At least on one side. A Michigan car if I remember correctly.

Doors on two door hardtops/converts are longer of course and sedans have framed windows. Trunk lids, in general, are the same for the body style. The length difference is in the panel between the rear window and the leading trunk edge. Tho, this varies on some models.

I have a 40 Studebaker that is presently being transformed from a four door sedan to a convert. Windshield/cowl laid back a few degrees. Lengthened front doors. Rear doors welded to body. Upper panel from trunk to passenger area lowered/lengthened. Fabricated top well. With a modified early Mustang convert top mechanism.

The car is on hold at the moment. I will post pics. When I get back to working on it. Moving, is taking all my time and energy at the moment.
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Old 03-04-2005, 02:56 PM
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I have been trying to find technical drawings so I can see exactly what modifications will be necessary to make as true a replica as I can to the factory convertible. I don't expect everything to be perfect but I want to get it as close a possible.

In what order did you (or will you) make the modifications on your studebaker?

I am starting with a solid 4dr sedan but with rotten rockers (inner and outer on both sides) and rotten floor sections between the front and rear seat risers each side of the driveline tunnel.

So, I have to cut out the rockers anyway, and plan to fabricate new ones for the 2dr conversion.

I don't want to cut everything up without some kind of sequence of events in mind to keep everything going back together lined up and true.

Here's the sequence of events I have been thinking of.

I am planning on cutting out the old rockers and welding in a section of steel rectangular tube (about 75mm x 35mm) to replace the original inner rocker. I would leave fabricating an outer rocker until last.

I am then thinking of cutting the required section out of the rear doors that I will need to lengthen the front doors and at the same time allow me to cut out the pillar ready to be moved to it's new position (and the top section cut out to match the line of the top of the doors).

Then I would lengthen the front doors using the section of inner door structure cut from the existing rear doors and weld up new door skins.

I am then thinking of hanging the new doors and using them to reposition the pillars, clamping everything in place at first and checking gaps and clearances and such before tack welding the pillar and what remains of the rear door in place as a solid unit with the quarter panel, using the rectangular tube inner rocker to strengthen and line everything up before welding it all up permanently.

I would then make a pattern for the outer rocker and fabricate it from scratch, welding it in place last of all.

Then there is a lot of finishing work and no doubt a bit of filler to finish the job.

What do you think of this sequence of events? Am I going to run into any major problems doing it this way?

Ok, that's part of the battle. As I said, I am planning a retractable hardtop not a true convertible. I already have the mechanism designed and working as a computer model, so I'm going to leave that alone for now.

The roof will be in three sections, and will require lowering the whole trunk floor and relocating the fuel tank (not sure where yet) in order for the roof to fully retract. This also involves a lot of internal modifications to the trunk but that should all be fairly straightforward, especially as it is all hidden. It's the exterior work I am most concerned with right now.

The original trunk lid will be welded shut, and a new "trunk lid" cut a lot wider (to the top peaks of the quarter panels) and extending all the way to where it would meet the rear glass. This whole big section will hinge from just above the rear bumper.

I will be strengthening the inside of the body big time with tubular steel framing especially towards the back where I have to cut out a lot of existing structure.

I am fairly certain that the '54 convertible (and hardtop) had a longer panel between the trunk and rear glass as you mentioned may be the case, as with your stude. How do you plan to extend this panel? and where did you get your reference dimensions and so forth?

As I said ideally I would like to find some technical drawings or at least someone with a real convertible or hardtop and a measuring tape.

I think modifying the sedan roof to meet the longer trunk to glass panel could be a bit of a problem as it basically means shortening the whole roof. My thoughts on this would be to chop the roof 2 or 3 inches (from the bottom) which would effectively make it shorter and give me a nice chop. I would have to recess the rear glass rather than cut it as the bel Air has full wraparound rear glass.

My last question is to do with side window glass. As I am cutting off the window frames on all doors, I will somehow need to make hardtop/convertible glass fit in my modified doors (front and rear) and sort out how it's going to meet the roof and seal properly and so forth. Any input on this would be great as I am not sure how this worked on the original hardtops.

Finally, the chassis will get a big fat X member for added rigidity.

The more I think about it, the more I realize what a huge amount of work all of this is.

What is your take on it all? I don't mean wether or not to do it, as I have pretty much made my mind up about that, but about how you might do it?

Sorry for the essay, I wanted to explain things in a way that will hopefully make sense.
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Old 03-04-2005, 05:14 PM
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I personally would build the rockers and bracing first.

I extended my doors by cutting the front doors vertically 2" from the rear edge. I then cut the rear doors the required stretch amount+2" vertically from the front edge. I then used the cut sections from the right rear door on the back of left front door. This was tacked and a door post was welded in to latch the door. The remaining 2" piece(from the original front door cut) was then pieced up to the rear of the door opening (oposing sides) to give the correct door/body gap. This needed about a 9/16" wide vertical filler strip for the side skin. Then the whole rear door was welded solid to the body. The tops of the doors rounded and modified for glass. I did not make new sheet metal skins or rockers as mine were in great shape for a car that served as a chicken Koop!. Mig welder and careful spot welds.

As for the filler panel from the trunk to the top. I looked up the difference of body line from the coupes and converts of the era and decided the area should be lowered about 2". This required a pie cut along each side of the trunk area and lay the area down toward the passenger area. Then an eyeball dimension to the edge of the top well. This will give it a kind of "Vicky/Phaeton" look.

I then "dummied" the convert top mechanism in and made a header for the top of the windshield area. I haven't done the glass yet. Or the "J" channel seals for the window to top seals. Vertical window seal will be old Ford convert. The glass is flat so I just make patterns on "Masonite" and have my glass guy cut them. The orginal type glass vertical channels will work. If modified. Mine will have a 2" chop so the windows will set down in the doors enuff for support. I am going to use Honda power window mechanisms.

I don't envy the retractable hardtop tho!. LOTS O WORK!! The convertable thing is enuff for me. But it will make a $175.00 sedan into something worth a bit. I've been working at it a little at a time for a few years. Too many "Life" projects going on. One of my old girlfriends says it's "Hers" when it's finished.

Your fourdoor top has a different "Hump" contour towards the back. For rear seat headroom. But that can be modified while doing the chop. LOTS O WORK! LOTS O WORK!
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Old 03-04-2005, 11:39 PM
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Yep, yep yep, Lots o work for sure. but I think more and more people will attempt these mods as the value of original converts and hardtops continues to rise.

I once thought it would be possible to scratch build a entire '57 Chevy convertible body from reproduction metal, using the right jig and some creativity of course. I then got to thinking it makes more sense to start with some kind of backbone in place, and a "cheap" 4dr sedan would be a fine starting point for such a project.

Of course mine isn't my dream '57, but if I manage to pull off this '54 I would start thinking seriously about creating my dream car myself rather than work my whole life for the 100,000 I would need to get my hands on an original parts car (ok, not so slight exaggeration there, maybe 30,000 for a restorable complete conv but you know what I mean).

Thanks for the input, very helpful indeed. I would be very glad to see some pictures sometime.
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